Was that the 'cargo heat outflow valve' AB ?
Sounds right. Maybe you had to close it at TOD to keep the cabin from climbing as the power came back.
And, if you forgot to leave it open on the next leg, the hold would freeze.
As a measure of how far we've come, looks like the 787 doesn't use bleed air at all for airconditioning and pressurization. It's all electrical. And we all know how reliable the electrics are. Nothing can go wrong, go wrong, go wrong...
Kinda like back to the future with the L-188 engine driven compressors.